The invention pertains to a system for providing naturalistic illumination patterns. More particularly, the invention pertains to a system for providing gradual interior illumination changes that accurately mimic light transitions of the natural world.
Human and other animal species live under conditions of natural illumination, both indoors and outdoors. Solar, lunar, and skylight illumination, it is believed, provide an environmental fabric that serves as a guiding force for performance, physiology, psychology and mood. Through research, scientists have been able to learn a great deal about the rhythmic nature of bodily systems and their interaction with illumination patterns.
It is submitted that artificial indoor lighting regimens--epitomized by somewhat arbitrary electric lighting in windowless rooms--pose undue and severe challenges to the occupant, being likely to adversely affect the natural rhythms that influence human behavior. The problem has already become apparent in many non-human laboratory studies. The daily ingestive pattern of nocturnal rodents, for example, is substantially modified by the absence or presence of cyclic lighting (Terman, Behavioral Analysis and Circadian Rythms, In: Advances in Analysis Behavior, Chichester: Wiley, pp. 103-141 (1983)). Researchers at the National Marine Fisheries Laboratory, Department of Commerce, have observed that sudden transitions from darkness to bright light induce the behavioral equivalent of "panic" in the bluefish, and for this reason have specified gradual twilights for their aquarium (Olla, et al, A Large Experimental Aquarium System for Marine Pelagic Fishes, Transactions of the American Fisheries Society 96:143-150 (1967)).
Physiological events during gradual twilights may be active transducers of day-night synchronizing signals, and in outdoor field studies it is common to find species selectively activated at dawn and dusk hours (e.g., Kavanau, et al, Twilight Zeitgebers, Weather, and Activity of Nocturnal Primates, Folia Primatologia 26:67-79 (1976)). Given the opportunity--which is absent in tightly controlled, spatially isolated laboratory studies--many species appear actively to "seek" the twilight signal, and to avoid tonic exposure to high daytime illumination levels. For example, given an escape option, through use of an artificial darkened burrow, the nocturnal rat selects bright light only briefly each day, and actually receives more light during a dim nighttime phase (Lynch, et al, Indirect Effects of Light: Ecological and Ethological Considerations, Annals of the New York Academy of Sciences 453:231-241 (1985)).
Twilight illumination is believed to be especially critical. For example, the human retina itself appears to respond selectively to twilights. It is known that photoreceptive discs in the rod outer segments of many species "shed" in a temporal burst, and are digested by the pigment epithelium shortly after light onset each day under the sudden illumination transitions of the laboratory (LaVail, Rod Outer Segment Disk Shedding in Rat Retina: Relationship to Cyclic Lighting, Science 194:1071-1074 (1976)). Under constant darkness, the circadian distribution of such shedding is considerably more diffuse. The normal photoreceptor renewal process may well depend on synchronization by natural daylight signals and it is believed possible that conventional indoor light cycling may pose a hazard to retinal physiology. A recent demonstration of severe retinopathy in hospitalized premature infants under protracted artificial light (Glass, et al, Effect of Bright Light in the Hospital Nursery on the Incidence of Retinopathy of Prematurity, The New England Journal of Medicine 313: 401-404 (1985)) reinforces this concern.
The lighting arbitrariness of the laboratory finds analogues in everyday urban life, where general daylight deprivation as well as deviant and variable light-switching schedules are common. Recent research has clearly documented human sensitivity to ambient illumination factors, as exemplified in winter at northern latitudes where daylight is insufficient to forestall clinical depressions, sleeping disturbances, and work productivity disruptions (e.g., Rosenthal, et al, Seasonal Affective Disorder: A Description of the Syndrome and Preliminary Findings with Light Therapy, Archives of General Psychiatry 41:72-80 (1984)).
When buildings are designed, many competing needs must be taken into account. This is especially true in the design of lighting systems, where the needs of the people who live and work indoors have often been supplanted by other contingencies. The pressure toward energy conservation forces reductions in indoor light availability--sometimes even codified in industrial standards (Thorington, Spectral, Irradiance, and Temporal Aspects of Natural and Artificial Light, Annals of the New York Academy of Sciences 453:28-54 (1985)).
A great deal is now known about the quantity of light needed to perform a wide variety of visual tasks, as well as the quality of light, for example, in terms of glare. The Illumination Engineering Society of North America has codified this knowledge into a set of recommendations (Kaufman, et al., IES Lighting Handbook (1981)). Little is presently known, however, about the impact of temporal variations in illumination upon long-term human performance and productivity. Human health, comfort, and productivity may be enhanced under conditions that more closely simulate naturally available light (e.g., Corth, What is "Natural" Light?, Lighting Design and Application, April issue, 34-40 (1983)). The daylight spectrum can be fairly mimicked by both fluorescent and halogen lighting sources (e.g., Thorington, et al, Journal of the Illumination Engineering Society 1:33-41 (1971)) but the critical variable of naturalistic temporal variation has yet to be applied.
One well-known prior illumination technology is the use of windows. That link to outdoor illumination, providing both light and view, is thought to provide benefits both to health and comfort (e.g., Ulrich, View Through a Window May Influence Recovery from Surgery, Science 224:421 (1984)); Verderber, Windows and Well-Being in the Hospital Rehabilitation Environment, Arch. D. dissertation, Ann Arbor: University Microfilms (1982)). Worker discontent with windowless office spaces is well-known (Collins, Windows and People: a Literature Survey, Building Science Series 70, Washington, D.C.: National Bureau of Standards (1975)). The current development of major U.S. government and industrial earth-sheltered environments, in which people will live and work for extended periods exclusively under indoor lighting, underscores the importance of this problem.
Previous work on daylight simulation problems concentrated almost exclusively on the daytime segment with the solar disk fully exposed above the horizon (e.g., Treado, Solar Radiation and Illumination, National Bureau of Standards Technical Note #1148 (1981)). The twilight factor has been explored in a complex treatise by the Russian astronomer Rozenberg, Twilight: A Study in Atmospheric Optics, New York: Plenum Press, (Trans. from Russian)(1966), and an empirical generalization of the twilight signal as a function of the sun's angular distance below the horizon was included in Biberman, Levels of Nocturnal Illumination, Research Paper P-232, Institute for Defense Analysis, Research and Engineering Support Division (1966).
Previous attempts have been made to build naturalistic simulators of daily illumination patterns. The various output functions that have been produced from known systems have all differed arbitrarily from the outdoor situation. Several workers in this field have varied voltage to incandescent lamps, yielding both arbitrary dimming cycles and idiosyncratic spectral shifts (e.g., Graham, et al, A Device for Simulating Twilight in Studies of Animal Activity, Behavior Research Methods and Instrumentation 9:395 (1977); Allen, A Device Providing Gradual Transitions Between Light and Dark Periods in the Animal Room, Laboratory Animal Science 12:252-254 (1980)). A second design turns a large bank of fluorescent lamps on and off in discrete steps, eliminating the spectral shift, yet failing to match the desired temporal transition curve. Swade, et al, in Circadian Locomotor Rhythms of Rodents in the Arctic, The American Naturalist 101:341-464 (1967) used a rotating aluminum channel to gradually cover and uncover a fluorescent bulb, and Kavaliers, et al, in Twilight and Day Length Affect the Seasonality of Entrainment and Endogenous Circadian Rhythms of a Fish, Couesius plumbieus, Canadian Journal of Psychology 59:1326-1334 (1980) developed an elaborate system of motor-pulley driven filters to obtain a log-linear illumination transition. One well-known prior illumination system, the whole-room illuminator at the National Fisheries Lab, uses an extensive bank of bulbs which turn on and off in a stepping pattern. The National Fisheries Lab system requires much effort to maintain, and a more efficient alternative is greatly needed.
No known prior design has produced an adequately naturalistic illumination function with the ability to track the season and latitude. No known prior system has been able to control light levels below the civil twilight range, the latter being quite bright relative to nautical and astronomical light levels that are orders of magnitude lower, yet still quite easily perceptible. The lunar illumination factor has also not previously been successfully modeled, although it too may provide a potent biological signal. Further, previous work has not offered a satisfactory engineering design for use in either laboratories or in human living and working environments.
It is therefore an object of the invention to provide a twenty-four hour naturalistic illumination system for use in illuminating interior environments.
It is a further object of the invention to provide a naturalistic illumination system for determining expected outdoor illumination levels across seasons and latitudes.
It is a further object of the invention to provide a naturalistic illumination system for providing natural light changes within living, working and laboratory environments.